The objective of this proposal is to elucidate biochemical causes of muscle fatty acid oxidation defects in humans. Patients singled out for investigation will include those having increased fatty acid intermediary oxidation metabolites of CoA or carnitine or abnormal in vitro oxidation of 1-14C or U-14C-palmitate. Patients of particular interest will be those with the various dystrophies, since we have alrady determined that these subjects not only accumulate fatty acid intermediary metabolites, but also demonstrate defective oxidation of U-14C-palmitate. This finding suggests that the abnormality lies after the oxidation of the first carbon. Chain length specific acyl-CoA dehydrogenase (AD) proteins, the first step in intramitochondrial Beta-oxidation, will be studied in skeletal muscle of these patients and control subjects using an enzyme activity-based staining technique with polyacrylamide gel electrophoresis and also high performance liquid chromatography. Chain length specific enoyl-CoA hydratase and 3-ketoacyl-CoA thiolase activities will be studied in the same patients using appropriate long and short chain CoA derivates. These methods should allow localization of the intramitochondrial beta-oxidation defects in chain length specific enzymes.